The present invention relates generally to a method and apparatus for electro-plating a metal on a semiconductor substrate. More particularly, the present invention is directed to a method and apparatus for forming electrical contacts on the semiconductor substrate using a liquid conductor during the plating process. Alternatively, electrical contacts may be formed using an inflatable tube that has either been coated with a conductive material or contains a conductive object. Furthermore, the present invention provides a method and apparatus for dissolving/etching a metal layer from the substrate edge.
Plating is an important and necessary step in the high performance chip fabrication process. When plating, it is necessary to form a good ohmic contact with a seed layer on/or near a circumferential edge of a substrate. Different conventional techniques exist to accomplish this task. According to one technique, for example, a great number of contact fingers, upwards of 130, are used to form contacts with the seed layer on the circumferential edge of a wafer. The contact fingers, which are typically metallic, are coupled to the circumferential edge of the wafer in accordance with any known method.
FIG. 1A illustrates a top view of a conventional configuration showing contact fingers 12 coupled to the wafer 2 during the plating process. As illustrated, a large number of contact fingers 12 extending from a housing 11 are evenly distributed around the circumferential edge 7 of the wafer 2. The housing 11 has a ring shape corresponding to the shape of the circumferential edge 7 of the wafer 2. An electric potential (cathode) is then applied to the wires 13 or housing 11 that are further coupled to the contact fingers 12 within the housing 11. This, in turn, provides the electric potential to the circumferential edge 7 of the wafer 2, thereby allowing the wafer surface to be plated. Instead of using the contact fingers 12 as described above, the electric potential can be applied to the wafer using a ring conductor.
FIG. 1B illustrates a cross sectional view of a conventional plating apparatus as described with reference to FIG. 1A. An entire back face 6 of the wafer 2 rests against a conventional chuck 8, and a vacuum 10 is used to ensure that the wafer 2 is stationary with respect to the chuck 8 while loading and/or plating the wafer 2. Regions adjacent to the circumferential edge 7 of the front face 4 of the wafer 2 are coupled to the contact fingers 12 as described above. A plating solution, typically a metal solution, is flowed in the direction of arrow 18 to the front face 4 of the wafer 2. When an electric potential is applied between an anode electrode 19, and the circumferential edge 7 of the wafer 2, the front face 4 of the wafer can be plated with the metal species contained in the plating solution.
Contact fingers are critical components of the wafer plating process as they provide the necessary electrical potential to the wafer. However, conventional plating systems such as described above have many drawbacks and disadvantages. For example, during the plating process, metal from the plating solution may be electro-plated on the contact fingers, thereby generating contaminating particles. In addition, the electro-plated metal on the contact fingers increases contact resistance resulting in a high voltage drop and failure. Moreover, over time, the contact fingers are susceptible to corrosion and/or fatigue. Failure of such contact fingers then leads to non-uniform wafer plating, which may cause irreparable damage to the semiconductor wafer, thereby resulting in lost products and revenues for the manufacturer.
Thus, there remains a need for a semiconductor substrate plating method and apparatus that provides plating in a dependable and reliable manner. Accordingly, a more consistent method and apparatus for providing an electrical contact to a semiconductor substrate during plating is needed.
It is an object of the present invention to provide a method and apparatus that provides electric potential to the wafer using a liquid conductor.
It is another object of the present invention to provide a method and apparatus that plates the front face of the wafer while preventing the plating solution from reaching the back face and edge of the wafer.
It is a further object of the present invention to provide a method and apparatus that plates the front face of the wafer while preventing the liquid conductor from reaching the back face of the wafer.
It is yet another object of the present invention to provide a method and apparatus that recycles the liquid conductor.
It is a further object of the present invention to provide a method and apparatus that dissolves/etches a metal layer from the periphery of the wafer.
It is another object of the present invention to provide a method and apparatus that provides electric contacts to the wafer using an inflatable tube that has been coated with a conductive material.
It is a further object of the present invention to provide a method and apparatus that plates a semiconductor workpiece such as wafers, flat panels, and magnetic films in a reliable and dependable manner.
It is yet another object of the present invention to provide a more efficient method for establishing electrical contacts with the wafer.
These and other objects of the present invention are obtained by providing a method and apparatus that plates a semiconductor wafer using a liquid conductor as the electrical contacts. The present invention includes a liquid chamber for holding the liquid conductor during the plating process. The liquid conductor is stored in a reservoir and pump through an inlet channel to the liquid chamber. A tube is inflated to seal the back face of the wafer, and the liquid conductor is injected into the liquid chamber such that the liquid conductor makes contact with the circumferential edge of the wafer. An electric potential is applied to the liquid conductor. Then, a plating solution is applied to the front face of the wafer. After plating the wafer, the used liquid conductor is removed from the liquid chamber through an outlet channel. Subsequent wafers are processed, each time using a fresh liquid conductor.
Alternatively, the inflatable tube may be coated with a conductive material to form electric contacts with the circumferential edge of the wafer. In this embodiment, the liquid conductor is not needed.
A further implementation of the method and apparatus of the present invention is to provide an acid or etching solution to the chamber such that the metal layer on the periphery of the wafer can be dissolved/etched.